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From: kcarroll@utzoo.UUCP (Kieran A. Carroll)
Newsgroups: net.space
Subject: Re: Lunar landings, cold mining, launchings
Message-ID: <3468@utzoo.UUCP>
Date: Mon, 16-Jan-84 11:58:49 EST
Article-I.D.: utzoo.3468
Posted: Mon Jan 16 11:58:49 1984
Date-Received: Mon, 16-Jan-84 11:58:49 EST
References: <15313@sri-arpa.UUCP>
Organization: U of Toronto Zoology
Lines: 27

*

   I see a problem, with both of the suggestions given for "sifting" lunar
soil.  Both methods are ways of fluidizing the soil, to allow larger rocks
to sink far below the surface.  However, at least if the rocks and soil
are of similar densities, fluidizing the soil may make the larger rocks 
rise up, instead.  Simple experiment:  next time you're making instant
coffee, put a spoonful of sugar and one of coffee crystals into the cup,
before you add the water. Put the codffee in first, and the sugar afterwards.
To start with, the sugar is then above the coffee.  Now, shake the cup for a
couple of seconds.  If the coffee crystals are larger than the sugar grains,
you'll (probably) find that the coffe crystals tend to rise to the top
of the mix. I don't know what the relative densities are in this case, but
you'll find that this works for differen-sized particles of identical densities.
For example, if you (or your little brother) has a bag of marbles (remember
those?), put a coupl of big ones in the middle of a jar full of little ones.
After shaking, the big ones tend to rise to the top.  
   The reason I've heard for this is that, when shaken, the small particles
in these mixtures tend to fall into the small gaps underneath the large 
particles, making the large ones migrate upwards.  I don't know if the same
effect would be observed in the proposed lunar schemes, but I suspect that
it would.
   Question: just how deep is the lunar "soil"? (of course, it's not real
soil).

-Kieran A. Carroll
...decvax!utzoo!kcarroll